Massively damaged in Aliens and Alien3, the synthetic Bishop asked to be shut down forever. His creator, Michael Bishop, has other plans. He seeks the Xenomorph knowledge stored in the android's mind, and brings Bishop back to life-but for what reason? No longer an employee of the Weyland-Yutani Corporation, Michael tells his creation that he seeks to advance medical research for the benefit of humanity. Yet where does he get the resources needed to advance his work. With whom do his new allegiances lie?

Bishop is pursued by Colonial Marines Captain Marcel Apone, commander of the Il Conde and younger brother of Master Sergeant Alexander Apone, one of the casualties of the doomed mission to LV-426. Also on his trail are the "Dog Catchers," commandos employed by Weyland-Yutani.

Who else might benefit from Bishop's intimate knowledge of the deadliest creatures in the galaxy?